1. Field of the Invention
The invention relates to respiratory treatment systems.
2. Description of the Related Art
Patients that suffer from sleep breathing disorders, such as obstructive sleep apnea (OSA), cheyne-stokes respiration, central apneas, or upper airway resistance syndrome (UARS), experience respiratory events during sleep. A respiratory event caused by OSA or UARS is usually characterized by a flow limitation in which the patient's upper airway becomes obstructed or restricted. During the respiratory event, the flow limitation causes the flow of gas through the airway to decrease progressively often until a respiratory effort related arousal occurs. The arousal clears the airway and the patient can experience inhalations and expirations that are abnormally large and sharp in relation to the patient's normal breathing flow.
In order to detect these types of respiratory events caused by upper airway restrictions, a signal representative of a rate of the flow of gas in an airway of a patient is typically monitored for changes that represent a flow limitation in the airway of the patient. Conventional methods of monitoring the flow rate to detect a flow limitation include analyzing the signal for a shape and/or pattern that is expected to be symptomatic of a flow limitation within the patient's airway, an absolute measurement of the signal, or relative changes in the flow rate. However, monitoring the flow of gas to the airway of the patient to detect flow limitations may lead to erroneous detections of respiratory events, and some respiratory events may not be detected at all. Consequently, a need exists for monitoring a patient for respiratory events with an enhanced accuracy.